1. Field of the Invention
The present invention relates to a nonreciprocal circuit element, such as an isolator and a circulator, for use in, for example, a microwave band, and relates to a communication device including the same.
2. Description of the Related Art
As a concentrated constant type isolator used for a mobile communication device such as a portable telephone, an isolator disclosed in Japanese Unexamined Patent Application Publication No. 11-97908 is known. As shown in FIG. 17, this isolator 200 substantially includes a resin terminal case 203, a lower metallic case 208, and an upper metallic case 204. These elements accommodate therein a permanent magnet 209, a center electrode assembly 213, matching capacitor elements C, and a resistance element R. The center electrode assembly 213 includes a center conductor 220 constituted of center electrodes 221 to 223 and a ground electrode 224, and a ferrite 230.
Windows 203b for accommodating the matching capacitor elements C formed in the resin terminal case 203, and an insertion hole 203a for accommodating the center electrode assembly 213 are formed at positions adjacent to each other. The side surface of the insertion hole 203a and that of each of the windows 203b communicate with each other via grooves 203c. 
As shown in FIG. 18, the center conductor 220 is arranged so that the center electrodes 221 to 223 and the ground electrode 224 thereof are integral with each other. The center electrodes 221 to 223 are each constituted of two parallel lines. These lines are each connected to the ground electrode 224 in a substantially linear configuration.
As shown in FIG. 17, the center electrode assembly 213 is obtained by the winding center conductor 220 around the ferrite 230. Specifically, the ferrite 230 is disposed on the ground electrode 224, and as shown in FIG. 19, the center electrodes 221 to 223 are folded substantially perpendicularly to the bottom surface of the ferrite 230. Furthermore, the center electrodes 221 to 223 are sequentially folded along the side surface and the top surface of the ferrite 230, and are placed on the top surface of the ferrite 230 with insulating sheets therebetween, thereby obtaining the center electrode assembly 213.
The center electrode assembly 213, the matching capacitor elements C and others are accommodated in the resin terminal case 203. At this time, since the insertion hole 203a and the windows 203b of the resin terminal case 203 communicate with each other via the grooves 203c, the center electrode 222 disposed on the side surface of the ferrite 230 is situated at a position adjacent to the hot-side electrode disposed over the entire top surface of a corresponding matching capacitor element C. Similarly, the center electrode 221 and another corresponding matching capacitor element C are also situated at positions adjacent to each other, although they are not shown in FIG. 19.
With the demand for miniaturization of mobile communication devices, the isolator 200 used in such communication devices has also been required to be miniaturized. As a result, the distance between the center electrode assembly 213 and the capacitor electrode of each of the matching capacitor elements C has been reduced. However, the reduction in distance between the center electrode assembly 213 and each of the matching capacitor elements C may cause a problem of short-circuiting. Because, due to displacement of the center electrode assembly 213 and/or at least one of the matching capacitor elements C, e.g. the edge 222a of the center electrode 222 and the capacitor electrode of the corresponding matching capacitor element C may contact each other, or solder balls adhered to the capacitor electrode of the corresponding matching capacitor element C may contact the edge 222a of the center electrode 222.
In order to overcome the problems described above, preferred embodiments of the present invention provide compact and a highly reliable nonreciprocal circuit element and communication device.
According to a preferred embodiment of the present invention, a nonreciprocal circuit element includes a permanent magnet, a ferrite having a first main surface to which a DC magnetic field is applied by the permanent magnet, a second main surface opposed to the first main surface, and a side surface substantially perpendicularly intersecting the first and second main surfaces, a center conductor having a ground electrode disposed on the second main surface of the ferrite, and a plurality of center electrodes that extend from the ground electrode and that are disposed so as to intersect each other at a predetermined angle on the first main surface of the ferrite through the side surface of the ferrite, matching capacitor elements that are disposed adjacent to a center electrode assembly including the ferrite and the center conductor, and that are electrically connected to the respective center electrodes, and a metallic member that accommodates the permanent magnet and the center electrode assembly. In this nonreciprocal circuit element, the height of the top surface of each of the matching capacitor elements is lower than that of the first main surface of the ferrite. Simultaneously, on the side surface of the ferrite, one edge of at least one of the center electrodes is located closer to the electrode of the corresponding matching capacitor element than the other edge of the center electrode. Furthermore, in a direction that is substantially perpendicular to the height direction of the ferrite, the second main surface side portion of the one edge of the center electrode is located farther from the electrode of the corresponding matching capacitor element than the first main surface side portion of the one edge of the center electrode.
Another preferred embodiment of the present invention, a nonreciprocal circuit element includes a permanent magnet, a ferrite having a first main surface to which a DC magnetic field is applied by the permanent magnet, a second main surface opposed to the first main surface, and a side surface substantially perpendicularly intersecting the first and second main surfaces, a center conductor having a ground electrode disposed on the second main surface of the ferrite, and a plurality of center electrodes that extend from the ground electrode and that are disposed so as to intersect each other at a predetermined angle on the first main surface of the ferrite through the side surface of the ferrite, matching capacitor elements that are disposed adjacent to a center electrode assembly including the ferrite and the center conductor, and that are electrically connected to the respective center electrodes, and a metallic member that accommodates the permanent magnet and the center electrode assembly. In this nonreciprocal circuit element, the height of the top surface of each of the matching capacitor elements is lower than that of the first main surface of the ferrite. Simultaneously, on the side surface of the ferrite, one edge of at least one of the center electrodes is located closer to the electrode of the corresponding matching capacitor element than the other edge of the center electrode. Furthermore, in a direction that is substantially perpendicular to the height direction of the ferrite, the central portion between the first main surface side portion and the second main surface side portion of the one edge of the center electrode is located farther from the hot-side capacitor electrode of the corresponding matching capacitor element than either of the first main surface side portion and the second main surface side portion of the one edge of the center electrode. Herein, each of the center electrodes may be branched into a plurality of lines on the side surface of the ferrite, and the branched lines may be disposed on the first main surface of the ferrite.
With these arrangements, the plurality of center electrodes disposed on the first main surface does not need to change the intersecting angle between them, thereby preventing the electrical characteristic of the nonreciprocal circuit element from being deteriorated. On the other hand, the center electrodes disposed on the side surface of the ferrite are each arranged so that the electrode width on the side where a corresponding matching capacitor element is disposed, that is, the electrode width on the second main surface side portion of the ferrite is reduced into a taper shape, or the central portion thereof between the first main surface side and the second main surface side is formed into a substantially V-shaped configuration, thereby locating the center electrode farther away from the electrode of the corresponding matching capacitor element than in the related case. This prevents the center electrodes disposed on the side surface of the ferrite and the electrodes of the respective matching capacitor elements from electrically connecting with each other.
Preferably, the shapes of the center electrode portions disposed on the side surface of the ferrite are each bilaterally symmetrical. Thereby, the bending stress to be applied to the center electrodes is uniformly applied in the width directions of the center electrodes, so that the center electrodes are correctly disposed on the first main surface through the side surface of the ferrite.
It is preferable that a nonreciprocal circuit element according to preferred embodiments of the present invention further includes a resin terminal member having a concave portion for accommodating the center electrode assembly and the matching capacitor elements. It is also preferable that each of the center electrodes disposed on the side surface of the ferrite be arranged so that the second main surface side portion thereof has a taper width that is narrower than the taper width of the first main surface side portion thereof, and that grooves each fitted to the taper shape of the center electrode are provided in the side wall of the concave portion of the resin terminal member. This improves the efficiency of work of inserting the ferrite and the center electrodes into the concave portion in the resin terminal case.
The present invention also provides a communication device that allows the implementation of a compact and high-reliability communication device by including the above-described nonreciprocal circuit element according to various other preferred embodiments of the present invention.
The above and other elements, characteristics, features, and advantages of the present invention will become clear from the following detailed description of the preferred embodiments of the invention in conjunction with the accompanying drawings.